According to the U.S. Census Bureau, the county has a total area of 1,596 km² (616 mi²). 1,567 km² (605 mi²) of it is land and 30 km² (12 mi²) of it is water. The total area is 1.88% water.
As of the census2 of 2000, there are 654,880 people, 266,294 households, and 166,167 families residing in the county. The population density is 418/km² (1,083/mi²). There are 288,231 housing units at an average density of 184/km² (476/mi²). The racial makeup of the county is 70.10% White, 23.27% Black or African American, 0.48% Native American, 1.28% Asian, 0.18% Pacific Islander, 2.43% from other races, and 2.25% from two or more races. 5.37% of the population are Hispanic or Latino of any race.
There are 266,294 households out of which 29.90% have children under the age of 18 living with them, 43.40% are married couples living together, 14.70% have a female householder with no husband present, and 37.60% are non-families. 31.20% of all households are made up of individuals and 9.90% have someone living alone who is 65 years of age or older. The average household size is 2.42 and the average family size is 3.05.
In the county the population is spread out with 25.80% under the age of 18, 9.10% from 18 to 24, 31.10% from 25 to 44, 21.50% from 45 to 64, and 12.50% who are 65 years of age or older. The median age is 35 years. For every 100 females there are 92.90 males. For every 100 females age 18 and over, there are 89.00 males.
The median income for a household in the county is $39,277, and the median income for a family is $48,435. Males have a median income of $35,798 versus $27,403 for females. The per capita income for the county is $20,788. 11.90% of the population and 9.00% of families are below the poverty line. Out of the total people living in poverty, 16.40% are under the age of 18 and 8.70% are 65 or older.